The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
In order to increase the fuel economy of motor vehicles, it is desirable to stop the engine during certain circumstances, such as when stopped at a red light or idling. However, certain conditions can inhibit the start/stop of the engine. For example, the hydraulic fluid within the accumulator may have a lower temperature than the hydraulic fluid within the transmission when ambient temperatures are relatively low, because the accumulator is typically located outside of the transmission. If the hydraulic fluid within the accumulator is too far below the temperature of hydraulic fluid within the transmission, the engine start/stop may be prevented from occurring, or if the start/stop occurs, the transmission performance may not be optimal.
Therefore, there is a need in the art for a system and method for controlling the temperature of hydraulic fluid located within the accumulator to enable proper use of engine start/stop techniques.